TPO 40 Lecture 3（文本在APP页面简介处）

学托福联系V: bravoyouth

Listen to part of a lecture in an environmental science class.

Professor

Now, over the next few weeks, we're gonna focus on carbon, and it's role in what's known as the greenhouse effect. Everyone knows what that is right? But let's make sure anyway. Yes, Carly.

Female Student

The greenhouse effect is when the gases in Earth's atmosphere act like the glasses in a greenhouse or hot house, they trap in heat, which warms up the Earth.

Professor

Gases like?

Female Student

Uh, water vapor, carbon dioxide.

Professor

Right, carbon dioxide, we hear a lot about carbon these days, no? Carbon emissions, carbon burning, leaving a carbon footprint. So it'd be easy to assume that any forms of carbon burning is necessarily a bad thing. But the fact is it's not quite that simple. So we're gonna focus today on the difference between good, bad, and well, the not so bad, the “potentially OK” carbon burning.

OK, good carbon burning, well, we all have a personal stake in this, because burning carbon is the basis of life. We wouldn't be here, if we ourselves weren't burning carbon. Uh, basically all living things burn carbon to survive. Usually this happens at the cellular level, and what's burnt is carbon in the form of sugars, glucose. Oxygen gets chemically combined with sugar in the cells, and the energy produced from that reaction is then used to power our cells. So just by breathing, you could say we are all guilty of carbon emission and contribute to the amount of carbon in the atmosphere.

Another thing about atmospheric carbon, it keeps us from freezing. Because without carbon and other greenhouse gases, our planet would be the same temperature as outer space. Around four degrees above absolute zero, and there’s nothing going on at that temperature, no possibility of life of any sort. So without atmospheric carbon, life couldn't existed on Earth.

Now, another thing to remember is that carbon is always being removed from the atmosphere. It gets used up. Largely it's consumed by plant life through photosynthesis. Also, it dissolves in the oceans, or gets stored deep in the ocean. You have shellfish that use the CO2 dissolved in the water to make carbonate shells, and when they die, they fall to the ocean floor. And the carbon gets sequestered down there. So, with all this carbon constantly been depleted from the atmosphere, we really need to keep carbon output up, to a certain point.

So, why all the bad press for burning carbon? Well, turns out it's the source of the

carbon been burned that's the key. It's in fact the burning of what we called“fossil carbon”, that creates the imbalance. The fossil fuels, the coal, oil, natural gas, these substances are all mined. We have to dig them up, or drill a well to release them. And this is the carbon that was in the atmosphere millions of years ago. So what happens is when we burn this carbon, OK, it doesn't release a whole lot

compared to the amount that's already in the atmosphere, but it adds to the pool. And over years it accumulates. Think of the atmosphere as a big bathtub, it is basically already filled to the rim with carbon, when we start adding fossil carbon into the mix, it starts to spill over.

That being said, there’s actually a category that's in between. What we called bio-mass fuels, and probably the most common one is wood. Another example, on the North American plains, the native Americans used to collect buffalo droppings to burn. And in Ireland they cut up pit from bogs, and they burn that. So, what's the big distinction between this and fossil carbon? Bio-mass carbon is what we might call “current carbon”, it's always going in and out of the atmosphere. So, if we burn one of these fuels, we are putting its carbon into the atmosphere, right? But in a balanced system, somewhere else in the word the same amount of carbon is going back. It gets taken in by growing vegetation. So burning bio-mass fuel produces sort of “not-so-bad carbon”, in fact it can become good carbon, if we endeavor as a society as humanity, to allow forests to recover this carbon. If we don't say, pave all over the surfaces to prevent things from growing. So whenever we cut down a tree and burn its wood, we have to allow another tree to grow, to keep things in balance, that way you… you are carbon neutral.